1. Field of the Invention
The present invention relates to a liquid sealed vibration isolating device for use in an engine mount or the like for motor vehicles and more particularly, to the device capable of effectively reducing noises created due to a cavitation phenomenon.
2. Description of the Related Art
In the liquid sealed vibration isolating device of this type, negative pressure is developed instantaneously in a primary liquid chamber when the heavy load is applied, so as to cause the cavitation phenomenon that hydraulic liquid is partially vaporized, and then the noise is generated. In view of this, there are proposed various kinds of devices for reducing transmission of the noise. The vibration generated when bubbles due to the cavitation phenomenon burst is transmitted from a partition member to a second metallic fitting and then from the second metallic fitting to a vehicle body side, so that it is perceived as the noise.
Therefore, in order to block such noise, there is known the art that an elastic body is interposed between a fitting bracket to the vehicle body and the second metallic fitting in such a manner that the whole of liquid sealed structure is floatingly supported on the vehicle body to block the transmission of the vibration from the inside of the primary liquid chamber to the vehicle body (as an example, see a patent reference 1). There is also known the structure that floatingly supports the partition member though an elastic body (as an example, see patent references 2 and 3).    Patent reference 1: Japanese patent laid-open publication No. 2006-64069.    Patent reference 2: Japanese patent laid-open publication No. 2004-316723.    Patent reference 3: Japanese patent laid-open publication No. H03-107636.
In the case where the whole of liquid sealed structure is floatingly supported on the vehicle body in such a manner as in the above mentioned prior art, the vibration is not transmitted to the vehicle body even if the cavitation phenomenon occurs in the primary liquid chamber, so that it is possible to block the generation of the perceivable noise. However, since the whole of liquid sealed structure is subject to lateral movement, etc. due to deformation of the elastic body interposed in relation to the vehicle body fitting (bracket), the support of the whole of the liquid sealed vibration isolating device becomes unstable. Moreover, since the device becomes large and component parts are increased so as to incur the increase in cost, the improvement in these respects is required.
On the other hand, in the case where only the partition member is floatingly supported without floatingly supporting the whole of the device as above, the partition member is held between a portion of an insulator and an outer peripheral portion of a diaphragm, so that since a floatingly supported portion undergoes a load in the direction of compression, the value of spring is increased so as to decrease the degree of freedom of the tuning with respect to the rigid resonance of the floatingly supported partition member.
Moreover, when strong force is applied to the diaphragm in the case of caulking the end of the second metallic fitting, etc., the outer peripheral portion of the diaphragm is deformed much by compression so as to develop a change in the value of spring for floatingly supporting the partition member. Therefore, it is required to prevent the development of remarkable change in performance at the time of assembling. It is also required not to affect the sealing property.
Further, the above mentioned patent reference 2 has no structure for floatingly supporting the partition member by the outer periphery of a diaphragm, and the metallic fitting for caulking and fixing a ring integrally formed with the outer periphery of the diaphragm is united through a thin elastic layer with an outer cylinder portion which corresponds to the second metallic fitting. Therefore, the partition member is not possible to generate and is not designed to generate the rigid resonance for effectively blocking for example the frequencies of about 800˜4000 Hz as a practically considerable range (hereinafter, referred to as noise frequency range) of the frequency which is perceived as the noise, within a frequency range of vibration generated due to the cavitation phenomenon. Accordingly, there is required the structure capable of mounting the second metallic fitting securely, capable of effectively preventing the noise created due to the cavitation phenomenon, moreover, capable of making the device compact, further, capable of increasing the degree of freedom of the tuning, and capable of preventing the change in the value of spring when in assembling.
Further, since an end of the ring inserted in the outer periphery of the diaphragm is in direct contact with the partition member so that the other end of the ring presses the partition member strongly when the other end is assembled and fixed by bending the metallic fitting, there is a possibility that the elastic body for floatingly supporting the partition member is compressed and deformed to a great extent so as to bring about a change in value of spring. Thus, since there is difficulty in the fitting operation of the diaphragm at the time of assembling, it is required to make the assembling operation easy.
Further, in the example of the patent reference 3, a seal portion formed by an outer peripheral portion of a diaphragm is subject to elastic deformation, so that an assembling operation for fixing the diaphragm while maintaining a proper sealing property becomes difficult. Therefore, it is required that the assembling operation can be easily carried out while maintaining a high sealing property. The present invention is made to materialize such requirements.